The present invention relates to a plate type heat pipe, which is especially suitable as a cooling device for a small-sized computer, such as a notebook computer.
Various instruments, such as personal computers, or electric parts, such as semiconductor devices, mounted on electric and electronics appliances, such as electric power devices, inevitably generate heat to some extent when in use. The technique to cool such instruments and electric parts has become an important technical focus. Various methods for cooling electric parts (hereinafter referred to as xe2x80x9cparts to be cooledxe2x80x9d), are known and include, for example, a method for cooling the air temperature inside the instrument by fixing fans thereto, and a method for cooling the parts to be cooled by fixing a cooling body thereto.
Generally, a plate material made of an excellent heat transfer material such as copper or aluminum is applied to the cooling body fixed to the parts to be cooled. When fins for radiating heat are integrally formed (by cast or forging) to the plate material, the parts to be cooled can be further cooled. Such a cooling body is called a xe2x80x9cheat sinkxe2x80x9d.
Recent proposals in this field include a cooling body having a structure of a heat pipe, or a cooling body comprising a plate material having excellent heat transfer properties, such as a copper or aluminum, with a heat pipe further fixed thereto. When a cooling body having the structure of the heat pipe is used, a flat type heat pipe is preferable because of the ease by which it can be fixed to the parts to be cooled.
Although a heat pipe is, generally, circular pipe, as its name describes, a flat type (in flat plate shape) heat pipe is also known. In either kind of heat pipe, there is disposed a hollow space that is a passage for a working fluid within the heat pipe. Heat is transferred within the passage by a phase transition between evaporation and condensation of the working fluid enclosed in the space. The working fluid may be called an operating liquid, however, because it becomes vapor, it is hereinafter called a working fluid.
The heat pipe has a sealed hollow portion in which heat is transferred by the phase transition and the movement of the working fluid enclosed therein. Although heat is transferred, to some extent, by heat conduction through the container forming the heat pipe, the main heat transfer method arises from the heat transfer function of the working fluid inside the heat pipe.
The working fluid in the heat pipe is usually water, aqueous solution, alcohol and other organic solvent. Mercury also may be used as the working fluid in certain cases. As described above, because the heat pipe makes use of phase transition of the working fluid inside the heat pipe, a mixture of gases other than the working fluid sealed inside is preferably excluded upon manufacturing the heat pipe. Usually, carbonic acid gas and the like are mixed in the process of manufacturing the heat pipe or exist in the state of the melt in the working fluid.
There are many heat pipes in a cylindrical shape. However, recently a flat type heat pipe has been effectively used as a cooling apparatus appropriate for cooling electronic parts relating to power electronic fields. The flat type heat pipe is not necessarily limited to a flat plate type; a heat pipe having a bent portion may also be used, (hereinafter xe2x80x9ca plate type heat pipexe2x80x9d).
Because the plate type heat pipe has a flat plate shape it has an advantage over other heat pipes in that it can be thermally connected to the parts to be cooled without difficulty, for example, when electronic parts such as IC devices are cooled. A radiating heat fin can be fixed in wide area to the plate type heat pipe for more effective use.
In operation, at the heat absorbing side of the heat pipe, the heat conducted through the container that forms the heat pipe evaporates the working fluid. The generated vapor is transferred to the heat radiating side. At the heat radiating side, the vapor of the working fluid is cooled to return to a liquid phase. The working fluid thus returns to the liquid phase and moves again (circulates) to the heat absorbing side. The heat is transferred by the above phase transition of movement of the working fluid.
In the case of a gravity type heat pipe, the working fluid, being in liquid phase by a phase transition, moves to the heat absorbing side by the function of gravity or capillarity. In this case, the heat absorbing side may be placed at a lower position than the heat radiating side.
It is known that the plate is shaped so that the parts to be cooled, such as electronic parts, can be easily contacted in wide area therewith. A plate type heat pipe has been proposed that is formed by welding two flat plates so as to have a sealed hollow portion therebetween. A plate type heat pipe has also been proposed that is formed by joining two flat plates with a release agent partially painted thereon, and pressurizing the joined flat plates to form a sealed hollow portion therebetween. More specifically, the portion painted with release agent expands to form a sealed hollow portion, and the like.
However, although the above-mentioned plate type heat pipe has a flat shaped hollow portion therein, the working fluid moves in multiple directions, thus the heat is not effectively transferred from the heat absorbing side to the heat radiating side.
Incidentally, in case the heat pipe is applied to a cooling mechanism of electronic parts, when the heat absorbing side of the heat pipe is placed below the heat radiating side thereof (hereinafter referred to as xe2x80x9cbottom heat modexe2x80x9d), the circulation of the working fluid by gravity can be expected. Accordingly, when electronic parts installed in a steady state inside an apparatus are cooled, it is preferable to place the heat absorbing side below the heat radiating side of the heat pipe. However, this kind of fixed allocation of the heat absorbing and heat radiating sides prevents a free design of the cooling mechanism using the heat pipe.
When a moving machinery and apparatus, a portable electric machinery and apparatus, or an electric control machinery and apparatus fixed to an overhead wire or the like is used, it is expected that the relative location of the heat absorbing side and the heat radiating side will vary. When the heat absorbing side of the heat pipe is placed over the heat radiating side thereof (hereinafter referred to as xe2x80x9ctop heat modexe2x80x9d), the circulation of the working fluid by gravity can not be expected, thus causing the situation in which the amount of the working fluid is short in the heat absorbing portion, or so called over-boiling.
Even if the top heat mode is applied, when the difference in height between the heat radiating side and the heat absorbing side, or the distance therebetween is small, the above-mentioned problem in relation to the shortage of the working fluid in the heat absorbing portion does not result. However, since the heat pipe is used mainly for the purpose of transferring heat, many times the heat radiating side is required to be separate to some extent, from the heat absorbing side. The limitation that the heat radiating side should be placed near the heat absorbing side restricts the extension in which various machinery and apparatus having a cooling mechanism may be used or operated.
The object of the present invention is, therefore, to provide a plate type heat pipe that maintains excellent functionality even in the top heat mode, and, furthermore, effectively controls the heat transfer by the working fluid in the intended directions.
In order to attain the above object, there is provided a preferred embodiment of a plate type heat pipe of the present invention, that comprises a sealed plate type metallic heat pipe having multiple independent through holes which run through the inside of said heat pipe, each of said through holes being connected in fluid communication at both ends thereof, a working fluid being enclosed in said through holes and wire or wire mesh being disposed in at least one of said through holes.
There is provided another embodiment of the plate type heat pipe of the present invention, wherein said wire or wire mesh comprises a wire material having a polygonal section.
There is provided another embodiment of the plate type heat pipe of the present invention, wherein said wire material of said wire or wire mesh has grooves formed on a surface thereof.
There is provided an additional embodiment of the plate type heat pipe of the present invention, wherein said wire material of said wire or wire mesh comprises a twisted wire.
There is provided another embodiment of the plate type heat pipe of the present invention, wherein said wire material of said wire or wire mesh is inserted into said through holes in a spiral manner.
There is provided an additional embodiment of the plate type heat pipe of the present invention, wherein a total section of said wire material of said wire or wire mesh occupies 5 to 40% of a total section of said through holes.
There is provided an additional embodiment of the plate type heat pipe of the present invention, wherein said wire or wire mesh comprises a wire material with grooves formed on a surface thereof.
There is provided another embodiment of the present invention, wherein said wire or wire mesh comprises a twisted wire.
There is provided another embodiment of the present invention, wherein said wire or wire mesh is inserted into said through holes in a spiral manner.
There is provided another embodiment of the present invention, wherein a section of said wire or wire mesh occupies 5 to 40% of a total section of said through holes.
There is provided an additional embodiment of the present invention, wherein a part of partition wall separating each of said through holes is removed near each end portion of said multiple through holes so as to connect said multiple through holes and close said each end portion.
There is provided an additional embodiment of the present invention, wherein a cap portion is joined near each end portion of said through holes so as to connect each of said through holes.
There is provided another embodiment of the present invention, that comprises a plate type heat pipe manufactured by the steps of: preparing a pipe having a plurality of independent through holes and a plurality of partition walls, said through holes extending in a longitudinal direction through an inside of said pipe, and defining end portions on opposite ends thereof, said plurality of partition walls being positioned in such a manner that each of said plurality of through holes is separated from every other through hole by one of said plurality of partition walls; removing part of said plurality of partition walls in both said end portions; closing one of said end portions so as to connect each of said plurality of through holes through removed partition walls; disposing one of a movable straight wire and a movable straight wire mesh extending along an axis of said through hole in each of said plurality of through holes in such a manner that a narrow space is formed between said walls forming said through holes and a side portion of said straight wire or wire mesh so as to cause sufficient capillary action between said wall forming said through hole and said straight wire or wire mesh, and receiving working fluid, then, closing the other end of said portions so as to connect each of said plurality of through holes, thus forming a container of a plate type heat pipe; and sealing said container receiving said working fluid.
There is provided another embodiment of the present invention, that comprises a plate type heat pipe, comprising: an extruded pipe having two ends and having a plurality of through holes defined by a plurality of longitudinally extending partition walls having portions removed at the ends of said pipe; a working fluid received in said pipe; two end caps, one positioned at each end of said pipe to hermetically seal said pipe, the working fluid in one through hole communicating with the working fluid in another through holes s a result of said removed portions of said partition walls; one of a non-porous, straight wire and non-porous, straight wire mesh movably positioned within said through hole such that a narrow space is formed between an inner wall of said partition wall forming said through hole and a side portion of said straight wire and wire mesh so as to cause sufficient capillary action.